The present invention relates to an optical device, and more particularly to a temperature compensated optical device.
It is known that a fiber Bragg grating may be passively mechanically temperature compensated so as to be xe2x80x9cathermalxe2x80x9d, i.e., substantially insensitive to changes in temperature, such as that described in U.S. Pat. No. 5,042,898, entitled xe2x80x9cIncorporated Bragg Filter Temperature Compensated Optical Waveguide Devicexe2x80x9d, to Morey, et al. However, such techniques require complicated mechanical packaging and are costly to manufacture. Also, such techniques may exhibit optical fiber attachment problems such as creep and hysteresis. Further, such techniques do not provide the ability to easily dynamically tune the grating wavelength to a desired wavelength.
Alternatively, it is also known to actively adjust the strain on a grating to compensate for changes in temperature, such as by using a closed loop controller that measures temperature and adjusts the strain on the grating accordingly. However, such techniques require active components to compensate for temperature changes, which increase complexity and cost and reduce reliability of the device.
Thus, it would be desirable to have a optical Bragg grating based package that is substantially insensitive to changes in temperature that has a simple construction and has low manufacturing cost.
Objects of the present invention includes provision of a passive optical a thermal package that has a simple construction and is low cost.
According to an embodiment of the present invention, a temperature compensated optical device comprises an optical element having at least one grating disposal therein along a longitudinal axis of said optical element the grating has a characteristic wavelength that varies with ambient temperature and upon the exertion of axial compressive force applied to the optical element the optical element is made of an element material having an element coefficient of thermal expansion (CTE). A spacer is disposed adjacent to an axial end of said optical element and made of a spacer material having a spacer CTE and that is larger than the element CTE. A housing is arranged with the spacer and the optical element such that at least a portion of the spacer and the optical element are in compression over an operational temperature range. The housing has a housing CTE that is less than said spacer CTE. Further, the characteristic wavelength changes less than a predetermined amount over said operational temperature range.
According to another embodiment of the present invention, a temperature compensated optical device comprises an optical waveguide having a cladding and a core disposed along a longitudinal axis of the optical waveguide. The optical waveguide further includes at least one grating disposed within the core. The grating has a characteristic wavelength that varies with ambient temperature and upon the exertion of axial compressive force applied to the optical waveguide. The optical waveguide is of a material having a waveguide coefficient of thermal expansion (CTE). At least a portion of the cladding and the core of the optical waveguide have a transverse cross-section, which is continuous and is formed of substantially the same material. The at least portion of the cladding and the core of the optical waveguide have an outer transverse dimension of at least 0.3 mm. A compression device includes a first member and a second member. The first member includes a material having a first coefficient of thermal expansion (CTE), the second member including a material having a second coefficient of thermal expansion (CTE) that is different than the first CTE of the first member. The first and second members are arranged in thermally compensating relationship with the optical waveguide such that the characteristic wave length is maintained within a predetermined wavelength range over an ambient temperature range.
According to another embodiment of the present invention, a temperature compensated optical device comprises an optical waveguide having a cladding and a core disposed along a longitudinal axis of the optical waveguide. The optical waveguide further including at least one grating disposed within the core. The grating has a characteristic wavelength that varies with ambient temperature and upon the exertion of axial compressive force applied to the optical waveguide. The optical waveguide is of a material having a waveguide coefficient of thermal expansion (CTE). At least a portion of the cladding and the core of the optical waveguide have a transverse cross-section, which is continuous and is formed of substantially the same material. The at least portion of the cladding and the core of the optical waveguide has an outer transverse dimension of at least 0.3 mm. A compression device includes a first member and a second member. The first member includes a material having a first coefficient of thermal expansion (CTE). The second member includes a material having a second coefficient of thermal expansion (CTE) that is different than the first CTE of the first member. The compression device strains the optical waveguide in response to a change in ambient temperature such that the characteristic wavelength is maintained within a predetermined wavelength range over an ambient temperature range.
According to another embodiment of the present invention, a temperature compensated optical device comprises an optical waveguide having a cladding and a core disposed along a longitudinal axis of the optical waveguide. The optical waveguide further includes at least one grating disposed within the core. The grating has a characteristic wavelength that varies with ambient temperature and upon the exertion of axial compressive force applied to the optical waveguide. The optical waveguide is of a material having a waveguide coefficient of thermal expansion (CTE). The optical waveguide comprises an optical fiber having the grating embedded therein and a tube having the optical fiber and the grating encased therein along a longitudinal axis of the tube. The tube is fused to at least a portion of the optical fiber. A compression device includes a first member and a second member. The first member includes a material having a first coefficient of thermal expansion (CTE). The second member includes a material having a second coefficient of thermal expansion (CTE) that is different than the first CTE of the first member. The first and second members are arranged in thermally compensating relationship with the optical waveguide such that the characteristic wavelength is maintained within a predetermined wavelength range over an ambient temperature range.
According to another embodiment of the present invention, a temperature compensated optical device comprises an optical waveguide having a cladding and a core disposed along a longitudinal axis of the optical waveguide. The optical waveguide further includes at least one grating disposed within the core. The grating has a characteristic wavelength that varies with ambient temperature and upon the exertion of axial compressive force applied to the optical waveguide. The optical waveguide is of a material having a waveguide coefficient of thermal expansion (CTE). The optical waveguide includes a pair of opposing axial surfaces. At least a portion of the cladding and the core of the optical waveguide has a transverse cross-section, which is continuous and is formed of substantially the same material. A compression device includes a first member and a second member, The first member includes a material having a first coefficient of thermal expansion (CTE). The second member includes a material having a second coefficient of thermal expansion (CTE) that is different than the first CTE of the first member. The first and second members are arranged in thermally compensating relationship with the optical waveguide such that the characteristic wavelength is maintained within a predetermined wavelength range over an ambient temperature range.
According to another embodiment of the present invention, a temperature compensated optical device comprises an optical waveguide having a cladding and a core disposed along a longitudinal axis of the optical waveguide. The optical waveguide further includes at least one grating disposed within the core. The grating has a characteristic wavelength that varies with ambient temperature and upon the exertion of axial compressive force applied to the optical waveguide. The optical waveguide is of a material having a waveguide coefficient of thermal expansion (CTE). The optical waveguide has an outer transverse dimension such that the optical waveguide will not buckle over an operational temperature range. At least a portion of the optical waveguide has a transverse cross-section which is continuous and made of substantially homogeneous material. A compression device includes a first member and a second member. The first member includes a material having a first coefficient of thermal expansion (CTE). The second member includes a material having a second coefficient of thermal expansion (CTE) that is different than the first CTE of the first member. The first and second member are arranged in thermally compensating relationship with the optical waveguide such that the characteristic wavelength is maintained within a predetermined wavelength range over an ambient temperature range.
The present invention provides a substantial improvement over the prior art by providing an Bragg grating device that passively mechanically compensates for changes in temperature such that the grating wavelength does not substantially change over a predetermined temperature range. Also, the invention may contain one or more Bragg gratings, a pair of Bragg gratings configured as a Fabry Perot interferometer or resonator or Bragg grating reflector laser, a distributed feedback (DFB) laser, or an interactive laser, that exhibits minimal changes over temperature (e.g.,  less than 50 picometers). The invention may be used as a very stable grating wavelength reference over temperature. Alternatively, the invention may be tuned to the desired wavelength at which to behave athermally. Further, the invention temperature compensates the grating passively, i.e., without any active components or feedback control loops, thereby reducing complexity and cost.
The foregoing and other objects, features and advantages of the present invention will become more apparent in light of the following detailed description of exemplary embodiments thereof.